The invention relates to a method and a device for carrying out work or an object which is present under water, wherein persons make their way to said object under water and carry out said work in artificial light. Such a method can be used in particular when carrying out work on a shipwreck, but the method can also be used for carrying out other kinds of work under water, for example in a river or on the seabed. In this connection, the removal of undesirable objects, such as poison gas grenades present in the seabed may be considered.
When work is being carried out under water, visibility is often limited because the water contains solid particles, which are carried along by currents in the water. Another problem that occurs when carrying out work under water is the fact that there is often a current in the water. Thus, there is a continuous current in rivers, and work on the seabed is often impeded by a changing current caused by the tides.
When there is a current in the water, limited visibility ensues, tools and other objects may be carried along by the current, holes that have been dug in the bottom may fill up and, especially when the current is a changing current, the people who carry out the work may become disoriented. In the case of tidal currents, it is often possible to carry out work under water only during the short period of time during which there is no current.
The object of the invention is to provide a method and a device which make it possible to carry out work under water in an efficient manner.
In order to accomplish that objective, a cover is provided over the object, which cover in the main abuts the bottom on which or in which the object is present in surrounding relationship with respect to said object, which cover encloses a space in which persons can work and within which artificial lighting is provided, which cover comprises an entrance for admitting persons to said space. Thus, a space is provided round the object in which there is no current and in which an optimum environment can be created for carrying out work.
Preferably, clean water is supplied to said space, which can take place near the highest point of said space, which water is preferably filtrated. To that end, filters may be provided on the upper side of the cover, through which filters the water is passed. Outside the cover, the water is clearer near the upper side of the cover than near the bottom, so that this is a suitable place for drawing in water from the surrounding space.
In another preferred embodiment, water is supplied to said space by utilizing the flow of the water surrounding the cover. One side wall is thereby provided with a water inlet, whilst one side on the other side of the cover is provided with a water inlet. Only cleaned water can flow into the space through a filter mounted in said inlet. When there are changing currents, it is possible to use several inlets and outlets, which can alternately be opened and closed.
In one preferred embodiment, means are present for draining water from the space. Said means preferably comprise drain openings in the side wall of the cover, namely at a height of less than half, preferably less than one-quarter, more preferably less than one-eighth, of the height of the space under the cover. As a result, the water in the lower part of the space, which the level of pollution is usually highest, will be drained off, whilst clean water can be supplied on the upper side of the cover.
Preferably, the device is provided with a fixedly disposed pump, which is connected, via a flexible conduit, to a nozzle by means of which substance can be sucked from the space. In this manner the persons carrying out work can remove polluted water or sand at random places.
Preferably, a number of connecting points are present on the inside of the cover for connecting the flexible conduit thereto, in which connecting points said flexible conduit can be connected to the fixedly disposed pump.
Preferably, the cover is provided with a downwardly extending wall at its circumferential edge, which wall can be pressed into the bottom. When a layer of sand is present on the bottom, this is a very efficient manner of effecting a proper connection to the bottom.
Preferably, the cover is provided with suction anchors, by means of which the cover is pressed against the bottom. Such suction anchors are known per se and they are capable of pressing the edge of the cover against or into the bottom.
It is also possible to press the cover against the bottom by reducing the pressure under said cover in comparison with the pressure outside the cover. Naturally, this is only possible when the edge of the cover in the main abuts the bottom and when direct and indirect connections between the interior and the exterior of the cover, inter alia connections which take place via filters, are closed. When the pressure is reduced in this manner, the edge of the cover can be pressed down to extend into the bottom.
Preferably, a piece of a flexible material is secured to the edge of the cover which extends to a point near the bottom, which material can be provided between said edge and the bottom. The flexible material may comprise one or more compartments, which can be filled with a material having a higher specific mass than water, for example sand and/or gravel. In this manner it is possible to obtain a good connection to the bottom, in particular when the bottom is not flat and consists of stones, for example.
Preferably, means are present for limiting the pressure difference between the space under the cover and the surrounding space. Such a safety valve is capable of limiting the pressure difference in two directions, for example at a level of less than one per cent.
By keeping the pressure in said space slightly higher than that in the surrounding space, it is possible to prevent an undesirably large amount of water flowing into said space from the surrounding space, for example when opening a lock.
Preferably, a living space is present under or near said cover, which space is capable of accommodating persons. Air can be supplied to said living space, and the living space may be heated, whereby persons who carry out work can stay in said space from time to time. This is important in particular if work is being carried out at great depth, so that persons must follow a lengthy procedure in order to get to the water surface. In that case, they may even carry out work for several days on end without having to make their way to the water surface from time to time.
Preferably, the cover can be moved in floating position, wherein floating bodies are present near the circumferential edge (seen in plan view), which floating bodies are filled with air. It is possible thereby to move the cover even in very shallow water. In order to ensure that the cover will remain stable while being moved, the cover can be turned upside-down, that""s, floating in upside-down position, in which position the cover can be towed by a tugboat.
Preferably, the cover is moved up from the bottom by filling compartments which are present near the centrally positioned upper part of the cover with air. Said compartments are provided with pressure relief valves in order to allow air to escape from the compartments while the cover is rising, so that the air pressure in the compartments can decrease. This makes it possible for the cover to rise in the water in a stable position.
Preferably, an engine room is present in or near the cover, in which air can be compressed and/or electricity can be generated. It is also possible, however, to carry out such operations in a module which floats on the water surface, which module is connected to said space by means of the necessary hoses and conducting wires.
In order to obtain proper lighting of the space, lighting equipment is provided in the side walls of the cover, which lighting equipment consists of lamps which are mounted at a height of less than three-quarters, preferably less than half, of the height of said space. Since the persons who carry out the work are often positioned above the place where they are carrying out said work, illumination from the side is advantageous.
The outside of the cover, seen in sectional view of the cover, is preferably semi-circular, ellipsoid or oval, or shaped otherwise with a view to minimizing the flow resistance of the cover.
Further aspects of the invention and of the method, which can be used separately as well as in combination with each other, will be described by means of an embodiment and be defined in the claims.
Preferably, the inner side of the cover is provided, at least locally so, with light-reflecting means. This will enhance visibility within the cover. Said reflection can also be achieved by lining the cover with a lightly coloured, preferably practically white, material.